A cover has been installed over the fuel handling machine that will help remove fuel from the storage pool of unit 3 of the Fukushima Daiichi nuclear power plant in Japan. The removal of the fuel is scheduled to start in mid-2018.

The section of the reactor building that sheltered the service floor of unit 3 was wrecked by a hydrogen explosion three days after the tsunami of March 2011 – leaving the fuel pond exposed and covered by debris including many twisted steel beams.

Once the largest pieces of rubble had been removed, Tokyo Electric Power Company (Tepco) began construction of a separate structure to facilitate the removal by a remotely-operated crane of the 566 fuel assemblies from the storage pool. This 54-metre-tall structure includes a steel frame, filtered ventilation and an arched section at its top to accommodate the crane. Measuring 57m long and 19m wide, it is not fixed to the reactor building itself, but is supported on the ground on one side, and against the turbine building on the other.

Installation of the first of eight sections of the arched roof of the cover was carried out last August. The fuel handling machine and crane were installed in November.

Tepco announced today the final section of the arched roof had been put in place, about two weeks ahead of schedule. Removal of the fuel assemblies will be carried out from the middle of the year.

The fuel removed from unit 3 will be packaged for transport the short distance to the site’s communal fuel storage pool, but it will need to be inspected and flushed clean of dust and debris. end quote.

nearly 7 years later, the nuclear experts of the planet are only now ready to de fuel spent fuel pool 3. Ever since the disaster, this fuel pool, four stories high in the air, has been in at first a totally wretched state of damaged supports and now, a wretched state of rushed reinforcement. From the day of the disaster it has not been fit to carry out its task. Despite industry protests that the fuel pool was perfectly fine, the fact is no sane nuclear authority on earth would licence spent fuel pool 3 as fit to house spent fuel rods. But since 2011 it has carried on doing just that. With extreme urgency the best the nuclear crowd could do was take 7 years just to get ready to de fuel the fuel pool. Cheer? Claps? Hip Hurrah? nope.

JAN 20, 2018
ARTICLE HISTORY PRINT SHARE
Tokyo Electric on Friday said it had spotted what is almost certainly fuel debris in reactor 2 at the Fukushima No. 1 plant that shows its fuel assembly likely dropped through the pressure vessel.

While Tokyo Electric Power Company Holdings Inc. got a peek at lava-like objects that looked like melted fuel in reactor 3 last year, this is the first time it has located similar debris in reactor 2.

Tepco inserted a 13-meter pipe-shaped device with two cameras on its tip into a 12-cm utility hole in the primary containment vessel to capture images of the area directly beneath the pressure vessel, which holds the core.

One camera spotted a handle for the fuel rod assembly lying at the bottom of the PCV, surrounded by sediment.

This means “there must have been a hole big enough to let the fuel rod assembly fall out of the reactor, so we are almost certain that the sediment around it is fuel debris,” Tepco spokesman Takahiro Kimoto explained at a news conference at the utility’s headquarters in Chiyoda Ward.

Kimoto also said the image shows pebble-like objects that look similar to the fuel debris witnessed at the Three Mile Island facility in Pennsylvania after its partial core meltdown in 1979.

The fuel melted after the mega-quake and tsunami of March 11, 2011, knocked out all power to the Fukushima No. 1 plant, crippling its vital cooling systems.

As a result, some of reactor 2’s fuel rods apparently melted and penetrated the bottom of the 20-cm-thick pressure vessel before dropping to the bottom of the PCV.

Locating the fuel debris is crucial to decommissioning the crippled plant, which is expected to take more than three decades. Tepco plans to decide on a plan for removing the fuel in fiscal 2019.

This is the first internal probe of reactor 2’s primary containment vessel since February last year, when it inserted a rod about 10 meters long to capture images of the interior.

At that time, Tepco found some black sediment stuck to the steel grating beneath the pressure vessel but could not tell what it was.

Last July, the utility sent a robot inside reactor 3’s PCV, where it found what was believed to be melted fuel debris.

To estimate the beta- and gamma-ray doses in a brick sample taken from Odaka, Minami-Soma City, Fukushima Prefecture, Japan, a Monte Carlo calculation was performed with Particle and Heavy Ion Transport code System (PHITS) code. The calculated results were compared with data obtained by single-grain retrospective luminescence dosimetry of quartz inclusions in the brick sample. The calculated result agreed well with the measured data. The dose increase measured at the brick surface was explained by the beta-ray contribution, and the slight slope in the dose profile deeper in the brick was due to the gamma-ray contribution. The skin dose was estimated from the calculated result as 164 mGy over 3 years at the sampling site.

INTRODUCTION
The main fission products from the Fukushima Daiichi nuclear power plant (FDNPP) accident are 129mTe-129Te, 131I, 132Te-132I, 134Cs, 136Cs and 137Cs [1–4]. These radionuclides emit gamma rays and beta rays through β− decay. However, there are few studies about dose estimation from beta-ray irradiation following the FDNPP accident [5–7]. The beta-ray dose contributes to the whole-body dose among small biota, such as insects, plant leaves, and human skin. Therefore, beta-ray dose estimations are important for the risk assessment of the impact of the FDNPP accident (including on small biota) to clarify the effects of this large-scale radiological accident.

Retrospective dosimetry with brick samples has been used to evaluate the gamma-ray dose of the Hiroshima atomic bomb [8–10], the Chernobyl nuclear power plant accident [11–14], and the Semipalatinsk nuclear weapon testing [15, 16]. Recently, Stepanenko et al. [17] used retrospective dose evaluation of brick samples to estimate gamma-ray doses and perform beta-ray dose reconstruction for the FDNPP accident with a similar method to that used for a Hiroshima tile sample [18]. They used a single-grain quartz optically stimulated luminescence (OSL) method (similar to that of Ballarini et al. [19], although layer-by-layer consequences for very thin layers of the sample’s aliquots were used for analysis, with separate dose calibration for each quartz grain) with brick samples taken in 2014 from Odaka, Minami-Soma City, Fukushima Prefecture, Japan [17]. Dose enhancement near the surface of the brick was identified by the OSL measurements [17]. Stepanenko et al. suggested that the enhancement was caused by the beta-ray dose from the deposited fission products [17].

To establish the cause of the dose enhancement near the brick surface, we performed a Monte Carlo simulation of a small brick building with radionuclides uniformly distributed on the ground surface. The calculated results were compared with the data measured by Stepanenko et al. [17]. The depth profiles of the dose in the brick sample for beta rays and gamma rays were estimated separately, and the dose enhancement near the brick surface was discussed.

……

Calculated dose rate for beta and gamma rays
A 137Cs deposition density of 308 kBq/m2 and the ratio of each radionuclide to 137Cs deposition density taken from the literature [1] were used to obtain Ak for each radionuclide. The deposition densities for the seven radionuclides are listed in Table 2. The beta-ray dose rates on the brick surface and gamma-ray dose rate at a depth of 0.5 mm in the brick at a height of 80 cm are shown in Fig. 2a and b, respectively. 129m, 129Te contributed less to the gamma-ray dose rate, and accounted for the third and fourth largest contribution to the beta-ray dose rate. This is due to the small gamma-ray emission rate per decay of 129m, 129Te of <10%. The gamma- and beta-ray doses decreased by ~10% and ~30%, respectively, over 1 month. The calculated beta-ray dose rate decreased slower than the calculated gamma-ray dose rate……

Beck reported conversion factors for various radionuclides to estimate the air dose rate at a height of 1 m from the unit deposition density of radionuclides [25]. The initial gamma-ray air dose rates (15 March 2011) at a height of 80 cm from the ground for each radionuclide obtained by our calculations were compared with the values estimated by Beck conversion factors [25] interpolated at a relaxation depth of 0.65 g/cm2 (Table 2). The present dose rates were estimated to be 57% lower than those calculated by Beck conversion factors. The present dose rates were in-brick values in one of the walls of the brick building, whereas the Beck conversion factor values were free-in-air values. Therefore, the difference of 57% can be explained by shielding effects, whereby gamma rays from behind the building are neglected.

Cumulative dose
The cumulative dose over 3 years, from 12 March 2011 (Unit 1 explosion) to 19 March 2014 (brick sampling by Stepanenko et al.) and the dose rate change over time are shown in Fig. 3. The solid line shows the calculation result, the dashed histograms are the averaged calculation values for the measured sample thickness, and the open circles are Stepanenko’s data [17]. The calculation agreed well with the data measured by Stepanenko et al. in the region deeper than 10 mm. The results indicated that the cumulative dose deeper in the brick was due to gamma rays, and that the dose enhancement at the surface was dominated by the beta-ray contribution. The difference between the calculated and measured doses at the surface was about 2 standard deviations. A possible explanation might be connected with the contributions of low γ emission rate radionuclides, such as 89Sr, 127mTe-127Te, 140Ba-140La, etc. However, the trend in the dose increase at the brick surface was supported by the calculations. Therefore, the single-grain OSL measurement by Stepanenko et al. shows the advantage of dose estimations not only the cumulative gamma-ray dose but also the cumulative beta-ray dose. Thus, we concluded that the single-grain OSL method is a good tool for retrospective beta-ray dose estimation.

The calculated tissue dose at a brick depth of 50 μm was assumed to be a skin dose, and would be similar to a 70-μm tissue dose. The skin dose was estimated to be 164 mSv for 3 years at the sampling location.

CONCLUSION
To confirm the cause of the dose enhancement near the surface of a brick sample taken from Odaka, Minami-Soma City, Japan, a Monte Carlo calculation was performed using PHITS code and the calculated results were compared with measurements. The calculated results agreed well with previously published measured data. The dose enhancement at the brick surface in the measured data was explained by the beta-ray contribution, and the gentle slope in the dose profile deeper in the brick was due to the gamma-ray contribution. The calculated result estimated the skin dose to be 164 mGy over 3 years at the sampling location.

ACKNOWLEDGEMENTS
The authors are grateful to Dr Tetsuji Imanaka, Kyoto University, for his advice.

CONFLICT OF INTEREST
The authors declare that there are no conflicts of interest.

FUNDING
This research was supported by the Japan Society for the Promotion of Science KAKENHI Grant No. JP26550031 (April 2014–March 2017).

A large amount of radionuclides were released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) during the meltdowns after the great east Japan earthquake in March 2011, and the Uranium speciation remains unknown.
Ms. Asumi Ochiai (M2 student) and a team lead by Dr. Satoshi Utsunomiya of Department of Chemistry have uncovered and succeeded, for the first time, in the atomic-scale analysis of debris nano-fragments released from the FDNPP into the environment, which is a mixture of the nuclear fuels and the structure materials. This is a result of international collaborative research with Tsukuba University, Tokyo Institute of Technology, University
of Manchester, University of Nantes, and Stanford University.
“We discovered nano-fragments of an intrinsic U-oxide nanoparticles closely associated with radioactive cesium-rich microparticles collected within 4 km from the FDNPP,”says Utsunomiya. “They are UO2+X and isometric (U,Zr)O2+X with the U/(U+Zr) molar ratio ranging from 0.14 to 0.91. The results indicated the heterogeneous physical and chemical properties of debris at the nanoscale, reflecting the complex thermal processes within the FDNPP
reactor during the meltdowns. The meltdown processes were partially unraveled, but we still need to obtain more information until the day when the real debris is safely removed.” For further information, see “Uranium Dioxides and Debris Fragments Released to the Environment with Cesium-Rich Microparticles from the Fukushima Daiichi Nuclear Power Plant”, Environmental Science & Technology, Ochiai et al., DOI: 10.1021/acs.est.7b06309

Trace U was released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) during the meltdowns, but the speciation of the released components of the nuclear fuel remains unknown. We report, for the first time, the atomic-scale characteristics of nanofragments of the nuclear fuels that were released from the FDNPP into the environment. Nanofragments of an intrinsic U-phase were discovered to be closely associated with radioactive cesium-rich microparticles (CsMPs) in paddy soils collected ∼4 km from the FDNPP. The nanoscale fuel fragments were either encapsulated by or attached to CsMPs and occurred in two different forms: (i) UO2+X nanocrystals of ∼70 nm size, which are embedded into magnetite associated with Tc and Mo on the surface and (ii) Isometric (U,Zr)O2+X nanocrystals of ∼200 nm size, with the U/(U+Zr) molar ratio ranging from 0.14 to 0.91, with intrinsic pores (∼6 nm), indicating the entrapment of vapors or fission-product gases during crystallization. These results document the heterogeneous physical and chemical properties of debris at the nanoscale, which is a mixture of melted fuel and reactor materials, reflecting the complex thermal processes within the FDNPP reactor during meltdown. Still CsMPs are an important medium for the transport of debris fragments into the environment in a respirable form.

New evidence of nuclear fuel releases found at Fukushima
February 28, 2018, University of Manchester

Uranium and other radioactive materials, such as caesium and technetium, have been found in tiny particles released from the damaged Fukushima Daiichi nuclear reactors.

This could mean the environmental impact from the fallout may last much longer than previously expected according to a new study by a team of international researchers, including scientists from The University of Manchester.

The team says that, for the first time, the fallout of Fukushima Daiichi nuclear reactor fuel debris into the surrounding environment has been “explicitly revealed” by the study.

The scientists have been looking at extremely small pieces of debris, known as micro-particles, which were released into the environment during the initial disaster in 2011. The researchers discovered uranium from nuclear fuel embedded in or associated with caesium-rich micro particles that were emitted from the plant’s reactors during the meltdowns. The particles found measure just five micrometres or less; approximately 20 times smaller than the width of a human hair. The size of the particles means humans could inhale them.

The reactor debris fragments were found inside the nuclear exclusion zone, in paddy soils and at an abandoned aquaculture centre, located several kilometres from the nuclear plant.

It was previously thought that only volatile, gaseous radionuclides such as caesium and iodine were released from the damaged reactors. Now it is becoming clear that small, solid particles were also emitted, and that some of these particles contain very long-lived radionuclides; for example, uranium has a half-life of billions of years.

Dr. Gareth Law, Senior Lecturer in Analytical Radiochemistry at The University of Manchester and an author on the paper, says: “Our research strongly suggests there is a need for further detailed investigation on Fukushima fuel debris, inside, and potentially outside the nuclear exclusion zone. Whilst it is extremely difficult to get samples from such an inhospitable environment, further work will enhance our understanding of the long-term behaviour of the fuel debris nano-particles and their impact.”

The Tokyo Electric Power Company (TEPCO) is currently responsible for the clean-up and decommissioning process at the Fukushima Daiichi site and in the surrounding exclusion zone. Dr. Satoshi Utsunomiya, Associate Professor at Kyushu University (Japan) led the study. He highlights that: “Having better knowledge of the released microparticles is also vitally important as it provides much needed data on the status of the melted nuclear fuels in the damaged reactors. This will provide extremely useful information for TEPCO’s decommissioning strategy.”

At present, chemical data on the fuel debris located within the damaged nuclear reactors is impossible to get due to the high levels of radiation. The microparticles found by the international team of researchers will provide vital clues on the decommissioning challenges that lie ahead.